The marathon trial of two Libyans accused of the Lockerbie bombing resumes Tuesday in Camp Zeist, the Netherlands after a mid-summer break, with the verdicts still months away and no clear indication of how the judges might rule.

Since it opened May 3rd, the trial -- being conducted under Scottish law -- has heard in excruciating detail how Pan Am Flight 103 was blown out of the night sky over the sleepy Scottish market town of Lockerbie on December 21st, 1988.

All 259 people on the New York-bound Boeing 747 flight from London were killed, along with another 11 people on the ground, in the most notorious mid-air bombing in civil aviation history.

Abdel Basset Ali al-Megrahi, 48, and Al-Amin Khalifa Fhimah, 44, have both pleaded not guilty to charges of murder, conspiracy to murder, and intentionally destroying an aircraft.

When the trial got underway, it was expected that the most complex and costly murder trial in Scottish history -- taking place at a special Scottish court set up in a former US air base -- might run for a year if not longer.

But so much non-controversial evidence has since been stipulated that defence attorney William Taylor said the trial -- being heard by three senior judges without a jury -- could wrap up in a matter of months.

"The estimate of the length of the case is now one-third," said Taylor on July 25, when the trial adjourned for four weeks.

University of Glasgow law professor Fraser Davidson, who is monitoring the trial, said there is talk that the case might possibly wrap up before Christmas, if not in November.

"But things have been so uncertain in terms of timing in the trial so far that one would be rash to make too firm a prediction," he told AFP in a telephone interview.

Past glitches have included breakdowns in the court's computer system, complaints about simultaneous Arabic translation for the defendants, and the occasional lack of witnesses ready to testify.

Crown prosecutors alone had well over 1,000 witnesses lined up, ready to be flown to the Netherlands and put up in local hotels, waiting for their turn to take the stand.

The one-off jail -- fitted with a Muslim prayer room and satellite TV -- has been their home since Libyan leader Moamar Kadhafi agreed in 1998 to their extradition after several years of international sanctions.

In some of its most sensational testimony, the trial heard in June from Swiss businessman Edwin Bollier, whose Zurich-based firm Mebo is alleged to have made the Lockerbie bomb's electronic timing device.

Bollier testified that he had gone to Libya to deliver 20 timing devices, and that he saw some of them used at a desert testing range for "military aircraft bombs". He recalled that Libya was in conflict with Chad at the time.

He also said he had met Megrahi several times and believed him to be possibly related to Kadhafi, to whose regime Bollier had previously sold a vessel and communications gear.

But under cross-examination Bollier, 62, acknowledged having collaborated with the Stasi, the former East German secret service. He also said a "mystery man" had told him to write to Washington to point an accusing finger at Libya.

In the early days of the Lockerbie investigation, it was suspected the bombers might be Palestinian extremists working on behalf of Iranians seeking to avenge the US downing of an Iranian airliner over the Gulf.

Other testimony has seen the defence questioning the level of airport security in Malta and Frankfurt, Germany, through which the baggage bomb passed on its way to London's Heathrow airport -- BRUSSELS (AFP)